At their core, they're nearly identical, using the phone's camera to auto-focus on a barcode. That barcode is then matched to a product using an open source decoding library, ZXing, that was developed by Google engineers last year. (You can also search by product name.)

While these shopping apps share a back end, the front ends are distinct. Unfortunately, they all produced varying results that inconsistently found retail and online stores stocking common products like hand lotion, gum, and breakfast cereal.

Barcode Scanner doesn't even try to compare prices by seller, but instead lets you search Google for product listings. All three applications were best at finding books, CDs, and DVDs, but were weak at tracking down brick-and-mortar stores in the San Francisco Bay Area. For example, CompareEverywhere plotted Barnes & Noble stores on a map, but failed to find the Borders down the street, which also listed the books I scanned in their online store.

Of the three applications, Barcode Scanner best integrates Google technology by linking book searches to Google's Book Search arm. That, by extension, gives you access to all those searching, buying, and library-hunting services, albeit through a Web interface. We'd rather see those tools pulled into an easily-read UI.

By contrast, CompareEverywhere has the best community spirit and default discretion. If it can't find your barcode in the UPCDatabase it uses, it asks if you want to add your product. Its confirmation--a low buzz compared to the other two apps' shrill beeps--is also the least conspicuous if you're laying low while comparing DVD prices from a physical store. As I mentioned, CompareEverywhere also maps retail stores on its radar and can e-mail links to your gift ideas, shopping list, and wish list to whomever you choose.

Of the three, ShopSavvy has the best-looking interface that lets you easily scan barcodes with the camera or enter them by hand if the barcode is smudged. Like CompareEverywhere, you can add products to a wish list and read reviews. You can't yet share lists, but you can send yourself an alert when prices drop below a certain point. If only ShopSavvy pulled up more online and retail stores for the everyday products thrown at it. I was disappointed it didn't find a source for my favorite brand-name cereal anywhere.

CompareEverywhere has the most useful features and had the best success rate in my tests, though all three apps will have something to offer when and if they're able to fill in sparse retail databases for online and especially brick-and-mortar shops. It's a daunting task, but instrumental if the apps are expected to help a wide swatch of people nail down deals.

Jessica Dolcourt reviews smartphones and cell phones, covers handset news, and pens the monthly column Smartphones Unlocked. A senior editor, she started at CNET in 2006 and spent four years reviewing mobile and desktop software before taking on devices.